Activity的ViewRoot的创建过程(三)

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在这篇文章里, 我们分析一下W类的构造过程. W类是定义在ViewRootImpl类中的一个内部类, W类的定义如下:
    static class W extends IWindow.Stub
    由此可见,  W本质上是一个Binder本地对象, 其实这是会传给WindowManagerService的, WindowManagerService就是通过W来通知Activity对象执行一些操作.

    W的构造函数如下:
    W(ViewRootImpl viewAncestor) {
        mViewAncestor = new WeakReference<ViewRootImpl>(viewAncestor);
        mWindowSession = viewAncestor.mWindowSession;
    }
    由此可见, W拿着ViewRootImpl和WindowSession.
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我们分析一下ViewRootImpl的setView函数的实现:
1     public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
2         synchronized (this) {
3             if (mView == null) {
4                 mView = view;
5                 mViewLayoutDirectionInitial = mView.getRawLayoutDirection();
6                 mFallbackEventHandler.setView(view);
7                 mWindowAttributes.copyFrom(attrs);
8                 attrs = mWindowAttributes;
9                 // Keep track of the actual window flags supplied by the client.
10                 mClientWindowLayoutFlags = attrs.flags;
11
12                 setAccessibilityFocus(null, null);
13
14                 if (view instanceof RootViewSurfaceTaker) {
15                     mSurfaceHolderCallback =
16                             ((RootViewSurfaceTaker)view).willYouTakeTheSurface();
17                     if (mSurfaceHolderCallback != null) {
18                         mSurfaceHolder = new TakenSurfaceHolder();
19                         mSurfaceHolder.setFormat(PixelFormat.UNKNOWN);
20                     }
21                 }
22
23                 CompatibilityInfo compatibilityInfo = mCompatibilityInfo.get();
24                 mTranslator = compatibilityInfo.getTranslator();
25
26                 // If the application owns the surface, don't enable hardware acceleration
27                 if (mSurfaceHolder == null) {
28                     enableHardwareAcceleration(mView.getContext(), attrs);
29                 }
30
31                 boolean restore = false;
32                 if (mTranslator != null) {
33                     mSurface.setCompatibilityTranslator(mTranslator);
34                     restore = true;
35                     attrs.backup();
36                     mTranslator.translateWindowLayout(attrs);
37                 }
38                 if (DEBUG_LAYOUT) Log.d(TAG, "WindowLayout in setView:" + attrs);
39
40                 if (!compatibilityInfo.supportsScreen()) {
41                     attrs.flags |= WindowManager.LayoutParams.FLAG_COMPATIBLE_WINDOW;
42                     mLastInCompatMode = true;
43                 }
44
45                 mSoftInputMode = attrs.softInputMode;
46                 mWindowAttributesChanged = true;
47                 mWindowAttributesChangesFlag = WindowManager.LayoutParams.EVERYTHING_CHANGED;
48                 mAttachInfo.mRootView = view;
49                 mAttachInfo.mScalingRequired = mTranslator != null;
50                 mAttachInfo.mApplicationScale =
51                         mTranslator == null ? 1.0f : mTranslator.applicationScale;
52                 if (panelParentView != null) {
53                     mAttachInfo.mPanelParentWindowToken
54                             = panelParentView.getApplicationWindowToken();
55                 }
56                 mAdded = true;
57                 int res; /* = WindowManagerImpl.ADD_OKAY; */
58
59                 // Schedule the first layout -before- adding to the window
60                 // manager, to make sure we do the relayout before receiving
61                 // any other events from the system.
62                 requestLayout();
63                 if ((mWindowAttributes.inputFeatures
64                         & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
65                     mInputChannel = new InputChannel();
66                 }
67                 try {
68                     mOrigWindowType = mWindowAttributes.type;
69                     mAttachInfo.mRecomputeGlobalAttributes = true;
70                     collectViewAttributes();
71                     res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
72                             getHostVisibility(), mDisplay.getDisplayId(),
73                             mAttachInfo.mContentInsets, mInputChannel);
74                 } catch (RemoteException e) {
75                     mAdded = false;
76                     mView = null;
77                     mAttachInfo.mRootView = null;
78                     mInputChannel = null;
79                     mFallbackEventHandler.setView(null);
80                     unscheduleTraversals();
81                     setAccessibilityFocus(null, null);
82                     throw new RuntimeException("Adding window failed", e);
83                 } finally {
84                     if (restore) {
85                         attrs.restore();
86                     }
87                 }
88                
89                 if (mTranslator != null) {
90                     mTranslator.translateRectInScreenToAppWindow(mAttachInfo.mContentInsets);
91                 }
92                 mPendingContentInsets.set(mAttachInfo.mContentInsets);
93                 mPendingVisibleInsets.set(0, 0, 0, 0);
94                 if (DEBUG_LAYOUT) Log.v(TAG, "Added window " + mWindow);
95                 if (res < WindowManagerGlobal.ADD_OKAY) {
96                     mAttachInfo.mRootView = null;
97                     mAdded = false;
98                     mFallbackEventHandler.setView(null);
99                     unscheduleTraversals();
100                     setAccessibilityFocus(null, null);
101                     switch (res) {
102                         case WindowManagerGlobal.ADD_BAD_APP_TOKEN:
103                         case WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN:
104                             throw new WindowManager.BadTokenException(
105                                 "Unable to add window -- token " + attrs.token
106                                 + " is not valid; is your activity running?");
107                         case WindowManagerGlobal.ADD_NOT_APP_TOKEN:
108                             throw new WindowManager.BadTokenException(
109                                 "Unable to add window -- token " + attrs.token
110                                 + " is not for an application");
111                         case WindowManagerGlobal.ADD_APP_EXITING:
112                             throw new WindowManager.BadTokenException(
113                                 "Unable to add window -- app for token " + attrs.token
114                                 + " is exiting");
115                         case WindowManagerGlobal.ADD_DUPLICATE_ADD:
116                             throw new WindowManager.BadTokenException(
117                                 "Unable to add window -- window " + mWindow
118                                 + " has already been added");
119                         case WindowManagerGlobal.ADD_STARTING_NOT_NEEDED:
120                             // Silently ignore -- we would have just removed it
121                             // right away, anyway.
122                             return;
123                         case WindowManagerGlobal.ADD_MULTIPLE_SINGLETON:
124                             throw new WindowManager.BadTokenException(
125                                 "Unable to add window " + mWindow +
126                                 " -- another window of this type already exists");
127                         case WindowManagerGlobal.ADD_PERMISSION_DENIED:
128                             throw new WindowManager.BadTokenException(
129                                 "Unable to add window " + mWindow +
130                                 " -- permission denied for this window type");
131                         case WindowManagerGlobal.ADD_INVALID_DISPLAY:
132                             throw new WindowManager.InvalidDisplayException(
133                                 "Unable to add window " + mWindow +
134                                 " -- the specified display can not be found");
135                     }
136                     throw new RuntimeException(
137                         "Unable to add window -- unknown error code " + res);
138                 }
139
140                 if (view instanceof RootViewSurfaceTaker) {
141                     mInputQueueCallback =
142                         ((RootViewSurfaceTaker)view).willYouTakeTheInputQueue();
143                 }
144                 if (mInputChannel != null) {
145                     if (mInputQueueCallback != null) {
146                         mInputQueue = new InputQueue(mInputChannel);
147                         mInputQueueCallback.onInputQueueCreated(mInputQueue);
148                     } else {
149                         mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
150                                 Looper.myLooper());
151                     }
152                 }
153
154                 view.assignParent(this);
155                 mAddedTouchMode = (res & WindowManagerGlobal.ADD_FLAG_IN_TOUCH_MODE) != 0;
156                 mAppVisible = (res & WindowManagerGlobal.ADD_FLAG_APP_VISIBLE) != 0;
157
158                 if (mAccessibilityManager.isEnabled()) {
159                     mAccessibilityInteractionConnectionManager.ensureConnection();
160                 }
161
162                 if (view.getImportantForAccessibility() == View.IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
163                     view.setImportantForAccessibility(View.IMPORTANT_FOR_ACCESSIBILITY_YES);
164                 }
165             }
166         }
167     }
168
第2行(ViewRootImpl->setView)会加锁
第3行(ViewRootImpl->setView)会保证一个ViewRootImpl只对应一个View
第4行(ViewRootImpl->setView)将成员变量mView设置成DecorView

第62行(ViewRootImpl->setView)会调用requestLayout()函数来进行一次layout, 而这是在加入到WindowManagerService管理之前进行的, 关于这部分的分析可以参考View的刷新部分的分析.
第71-73行(ViewRootImpl->setView)会调用WindowSession的addToDisplay函数将mWindow传给WindowManagerService, 关于这部分的分析可以参考Activity和WindowManagerService连接系列的文章.
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    我们来看一下PhoneWidnow的getDecorView函数的实现:
    public final View getDecorView() {
        if (mDecor == null) {
            installDecor();
        }
        return mDecor;
    }
    getDecorView函数如果发现mDecor还没有初始化过, 就会调用installDecor函数来构造一个DecorView